Electrical contact brushes

ABSTRACT

An electrical brush comprises a metal-and-carbon containing body and a metallic layer to which an electrical conductor is or may be secured and electrically connected. The metal-and-carbon containing body is sintered with the metallic layer in an area which is greater than the area at the connection of the electrical conductor to the layer.

United States Patent 72] inventor Colin Whiteheart Morden, England [21]Appl. No. 825,305

[22] Filed May 16, 1969 [45] Patented Aug. 24, 1971 [73] AssigneeMarganite Carbon Limited London, England [32] Priority May 23, 1968 [33]Great Britain [54] ELECTRICAL CONTACT BRUSHES 10 Claims, 7 Drawing Figs.

[52] 11.8. CI 310/249, 29/630 E, 310/251, 310/252 [51] Int. Cl 1101!39/36 [50] Field of Search 219/226; 245/247; 310/249, 251, 252, 253

[56} References Cited UNITED STATES PATENTS 1,053,881 2/1913 Scott eta]310/251 Primary Examiner-D. F. Duggan Assistant ExaminerB. A. ReynoldsAttorneyBa1dwin, Wight & Brown ABSTRACT: An electrical brush comprises ametal-and-carbon containing body and a metallic layer to which anelectrical conductor is or may be secured and electrically connected.The metal-and-carbon containing body is sintered with the metallic layerin an area which is greater than the area at the connection of theelectrical conductor to the layer.

ELECTRICAL CONTACT BRUSHES This invention relates to electrical contactbrushes and to the manner in which a flexible electrical conductor isattached to the'body of the brush.

It is known to attach a flexible conductor to a brush by inserting theconductor in a hole formed in the body of the brush and thereaftersecuring the conductor within the hole by means of, for example, solderor compressed metal, or a rivet, or by swagging the brush around theconductor. These methods are well established but they are not alluniversally applicable; consequently a particular method of attachmentmust be selected for a particular brush design or construction. Forexample, it is very difficult to drill a suitable hole if the brush isvery small. Also the various methods have their own particulardisadvantages. The use of compressed powders in a hole may not provideadequate securing strength when the conductor is subjected tointermittent vibration and shock. Soldering presents problem due to theshrinkage of the material when the solder cools. Swagging raises thebrush material density in the area at which the swagging takes place,and this represents a waste of expensive copper, for example, and it canalso lead to disintegration of the brush material at the swagging area.

The present invention seeks to overcome these disad-.

vantages.

According to the present invention an electrical contact brush comprisesa metal-and-carbon containing body, a metallic layer sintered with saidbody, and electrical conductor means secured to said metallic layer andelectrically connected therewith, said metallic layer having a greatertensile strength than that of said body.

The brush body may be made of a number of materials known in the art ofelectrical brush manufacture. Thus it may be selected from a wide rangeof materials going from a mixture of carbon with various metals oralloys (for example copper or copper with one or more additives such aslead, tin, manganese or silver), carbon/metal mixtures containing smallquantities of other additives such as nonconducting abrasives andlubricants including molybdenum disulflde and P.T.F.E., i.e.polytetrafluoroethylene, through to metals containing only small amountsof carbon and/or other additives.

The main purpose of this invention is to overcome the problemsencountered with brush designs wherein there is a weakness in the areaof the junction between the body and the flexible conductor andparticularly in the body portion immediately surrounding the junction.Therefore, whilst the invention might be applicable to almost allbrushes, it is particularly concerned with brushes whose bodyconstruction is such that problems have been encountered in usage due tofracture near the junction of the body with the flexible conductor.

Thus the metallic material of the layer sintered onto the body is chosento have a greater tensile strength than the material of the body (whichitself may contain a large proportion of metal), and the area of contactbetween the metallic layer and the body should be larger than the areaof contact between the flexible conductor and the metallic layer,thereby effectively spreading the load over a relatively large area ofthe body if any jerks are applied to the flexible conductor.

In one preferred embodiment of the invention the metallic layereffectively covers the face of the body of the brush opposite to theworking (electrical contact) face.

Examples of the present invention will now be described with referenceto the accompanying drawing in which:

FIG. I is a-side view of one embodiment of an electrical contact brush,

FIG, 2 is a view, in cross section, of another embodiment of anelectrical contact brush, and

FIGS. 3 7 illustrates varioussteps in the manufacture of an electricalcontact brush.

In the figures an'electrical contact brush comprises a body 1 havingattached thereto a metallic layer 2 to which is secured a flexibleelectrical conductor 3. The brush body 1 is composedprimarily of a metaland graphite and the metal canbe, for example, copper together withalloyconstituents known in the art. The metallic layer 2 can be composedof, for example, copper or iron, or a mixture thereof but the inventionis not limited to the use of such metals. The flexible conductor 3 maybe formed from thin electrically conductive metal strands of, forexample, copper. The strands can, of course, be formed from any othersuitable metal.

In the example illustrated in FIG. 1 the flexible electrical conductor 3is attached to a surface of the metal layer 2 by welding. The weldedjoint is indicated at 4. It is preferred that the welded joint is madeby using a pressure-resistance welding technique.

In FIG. 2 the flexible conductor 3 is secured to the metal layer 2 byforming a bore in the layer 2 and thereafter securing one end of theflexible conductor within the bore by tamping with, for example, copperparticles 6.

Although not illustrated the flexible conductor 3 can, if desired, beplaced in the bore and thereafter soldered to the metallic layer 2.

The brush body 1 is composed primarily of a metal and a graphite, andthe metal may be copper with alloy constituents known in the art.Copper, or any other suitable metal can be present up to percent of thetotal brush composition. A wide variety of materials may be used for thebrush body, for example, compositions of metal and graphite in the rangeof from 25 percent copper, 75 percent graphite to 95 percent copper, 5percent graphite, and the compositions may include lead, tin, zinc or acombination of these up to about 15 percent of the total composition sothat, at the extreme, the brush composition may consist of 95 percentmetal or alloy and 5 percent graphite. It will thus be realized that theactual brush materials themselves are not of prime importance but thepresent invention is particularly useful when it is necessary to attacha flexible copper conductor to a brush containing a major proportion ofmetal.

It is arranged that the surface area of contact between the metalliclayer 2 and the brush body 1 is larger than that between the flexibleconductor 3 and the metal layer 2. With this arrangement should theflexible conductor 3 be subjected to any form of tensile loading, theload per unit area on the body is comparatively reduced and certainlyless than what it would be if the conductor were attached directly tothe body.

It is preferred that the metallic layer 2 is formed and attached to thebrush body 1 by cocompacting and cosintering the layer material togetherwith the brush body material.

The compacting and sintering processes are illustrated schematically inFIGS. 3-7. FIG. 3 represents a compaction press which includes a die 7having a pair of reciprocal plungers 8 and 9. Metallic powders to formthe brush body 1 are placed in the die as shown in FIG. 4. The bottomplunger 8 is then lowered by a specified amount. Powders whichconstitute the metallic layer 2 are then put in the die 7 on top of theconstituent powders of the brush body 1. This is shown in FIG. 6. Thetop plunger 9 is then brought down to compress and so compact thepowders together and the compacted constituents are then sintered at asuitable temperature for a suitable period of time.

In one particular example of the present invention the followingmetallic powders were blended together with a small amount of dielubricant, stearic acid (zinc steareate was also suitable as the dielubricant):

78 parts by weight of mesh copper powder,

10 parts by weight of 200 mesh lead powder,

six parts by weight of 100 mesh manganese powder, and

six parts by weight of 200 mesh natural graphite.

The mixture of powders was put into the die of a compaction pressand onto the top of this powder was placed a measured quantity of I00 meshreduced sponge iron powder to form a layer of 5 mm. depth. The powderswere then cocompacted together at 10 tons per square inch pressure andwere cosintered at 840 for 1 hour in a suitable protected atmosphere.

It should be noted that the powders forming the brush body 1 can becompressed before the powders constituting the metallic layer 2 areplaced thereon. However, subsequent compaction does not provide a bondbetween the body and the layer as good as that of the first'mentionedprocess. Accordingly, the first process is preferred.

The cocompacting and cosintering processes provide an excellent physicaland electrical bond between the brush body and the metal layer. Thejoint between the flexible electrical conductor and the metallic layer,whether it be made by welding, tamping or soldering, is physicallystrong since the attachment is made between two metals. And since thesurface area at the interface between the metallic layer and the brushbody is larger than that between the flexible conductor and the layer'any tensile loading applied to the flexible conductor will bedistributed evenly over the rush at said interface.

What I claim is:

1. An electrical brush comprising a metal-and-carbon containing body, ametallic layer sintered with said body, said metallic layer comprising ametal other than any ingredient of said body, and electrical conductormeans secured to said metallic layer and electrically connectedtherewith, said metallic layer having a greater tensile strength thanthat of said body.

2. An electrical brush according to claim 1 wherein the surface area ofcontact at the interface between said metallic layer and said body isgreater than that between said metallic layer and said conductor means.

. metallic layer comprises copper.

.7. An electrical brush according to claim 1 wherein said metallic layerconsists essentially of a metal alloy.

8. An electrical brush according to claim 1 wherein said metallic layerconsists essentially of a mixture of copper and iron.

9. An electrical brush according to claim 1 wherein said body is acomposition essentially of copper and graphite in the range of from 25percentcopper, percent graphite to percent copper, 5 percent graphite.

10. An electrical brush comprising a body of sintered metaland-carbon; asintered metallic material layer, said metal-andcarbon of said bodybeing cosintered with the metallic material of said layer, said metallicmaterial layer comprising a metal other than any ingredient of saidbody; and electrical conductor means secured to said layer andelectrically connected therewith, said layer having a greater tensilestrength than said body.

1. An electrical brush comprising a metal-and-carbon containing body, ametallic layer sintered with said body, said metallic layer comprising ametal other than any ingredient of said body, and electrical conductormeans secured to said metallic layer and electrically connectedtherewith, said metallic layer having a greater tensile strength thanthat of said body.
 2. An electrical brush according to claim 1 whereinthe surface area of contact at the interface between said metallic layerand said body is greater than that between said metallic layer and saidconductor means.
 3. An electrical brush according to claim 1 whereinsaid conductor means comprises a flexible electrical conductor, saidflexible conductor being secured integrally to said metallic layer. 4.An electrical brush according to claim 1 wherein said metallic layerconsists essentially of a metal.
 5. An electrical brush according toclaim 4 wherein said metal is iron.
 6. An electrical brush according toclaim 1 wherein said metallic layer comprises copper.
 7. An electricalbrush according to claim 1 wherein said metallic layer consistsessentially of a metal alloy.
 8. An electrical brush according to claim1 wherein said metallic layer consists essentially of a mixture ofcopper and iron.
 9. An electrical brush according to claim 1 whereinsaid body is a composition essentially of copper and graphite in therange of from 25 percent copper, 75 percent graphite to 95 percentcopper, 5 percent graphite.
 10. AN electrical brush comprising a body ofsintered metal-and-carbon; a sintered metallic material layer, saidmetal-and-carbon of said body being cosintered with the metallicmaterial of said layer, said metallic material layer comprising a metalother than any ingredient of said body; and electrical conductor meanssecured to said layer and electrically connected therewith, said layerhaving a greater tensile strength than said body.